Web center-guiding apparatus

Abstract

An air-bearing center-guiding apparatus is disclosed for supporting and laterally center-guiding thin, flexible webs of paper or plastic under 15 mils in thickness. The apparatus comprises a web support and guide member 10 having an inner surface 58 and an outer web-facing surface 60. The web support and guide member 10 comprises a base member 14 for supporting an inner ring 22, an end cap 38, and a center ring 28 interposed therebetween. Parallel, circumferentially extending rows of circumferentially elongated and spaced-apart guide apertures 62 are provided in the web support and guide member 10 along edge regions of the web. The guide apertures 62 are formed between end surfaces 46 of the center ring 28 and interengaging end surfaces of the inner ring 22 and end cap rings 38. Each guide aperture 62 extends substantially perpendicular to the surface of the web and defines in cross-section an opening having a straight side and a curved side for directing jets of air against the web edges for developing a guiding force for holding lateral movement of the web to plus or minus 0.001 inch (0.0254 mm). A row of support apertures 56, separate from the guide apertures 62, is provided in the center ring 28 between the rows of guide apertures 62 to form an air-bearing for the web.

What is claimed is: 
     
       1. An air-bearing center-guiding apparatus for supporting and laterally center-guiding a thin web along a longitudinally extending web center line, wherein the web has longitudinally extending side edges defining a predetermined web width, comprising: an inner member having an inner end surface;   an outer member in alignment with the inner member and having an outer end surface;   a center member in alignment with and interposed between said inner and outer members and of a width substantially equal to said web width, said center member having a convex outer web-facing surface and opposite center end surfaces in mating engagement with said inner and outer surfaces;   a plurality of spaced-apart guide apertures formed at the interface between said center and surfaces and said inner and outer end surfaces and extended through said web-facing surface, said guide apertures being oriented substantially perpendicular to the web and arranged in a pair of parallel spaced-apart rows, each said guide aperture defining in cross-section an elongated aperture having a straight side and a curved side with one of said sides substantially in register with a side edge of said web and the other of said sides extended beyond said side edge, whereby each said elongated aperture is positioned substantially beyond said width of said web;   web-support means in said center member interposed between said rows of guide apertures and extended through said outer surface; and   a source of pressurized air coupled to said web-support means for directing air therethrough to form an air cushion below the web and coupled to said elongated guide apertures for directing jets of air therethrough against the web edges for forming localized web-guiding deformations on the web edges for laterally center-guiding the web along the web center line.   
     
     
       2. An air-bearing center-guiding apparatus according to claim 1, wherein said straight sides of said guide apertures are in register with the side edges of the web. 
     
     
       3. An air-bearing center-guiding apparatus according to claim 1, wherein said curved sides of said guide apertures are curved convexly outwardly from the longitudinally extending center line of the web. 
     
     
       4. An air-bearing center-guiding apparatus according to claim 1, wherein said curved sides of said guide apertures are curved concavely outwardly from the longitudinally extending center line of the web, with the apexes of said curved sides thereof substantially in register with the web edges. 
     
     
       5. An air-bearing center-guiding apparatus according to claim 2, wherein the web to be supported and guided is a flexible web of paper or plastic of a thickness under substantially 15 mils. 
     
     
       6. An air-bearing center-guiding apparatus according to claim 1, wherein the width of each guide aperture is substantially 6 mils and the length of each straight side is substantially 30 mils. 
     
     
       7. An air-bearing center-guiding apparatus according to claim 1, wherein said web-support means comprises a plurality of support apertures located substantially along the longitudinally extending center line of the web. 
     
     
       8. An air-bearing center-guiding apparatus according to claim 1, wherein said center member over which the web is guided is a fixed arcuate member having a leading section, an intermediate section and a trailing section, and wherein said web-support means comprises a pair of parallel, longitudinally extending rows of support apertures provided in the intermediate section for generating a predetermined volume of support air, said support apertures being arranged in spaced-apart relation in each row, and at least three parallel, longitudinally extending rows of further support apertures provided in said leading and trailing sections for generating a volume of support air greater than the predetermined volume, said further support apertures being arranged in spaced-apart relation in each row. 
     
     
       9. An air-bearing center-guiding apparatus according to claim 8, wherein said rows of support apertures are located substantially along the intermediate section of the arcuate member. 
     
     
       10. An air-bearing center-guiding apparatus according to claim 1, wherein the apparatus further comprises a base member having a first cylindrical shoulder, wherein said inner member is mounted on the first cylindrical shoulder, wherein said inner member has a second cylindrical shoulder, wherein the outer member has a third cylindrical shoulder, wherein the center member is mounted between said second and third cylindrical shoulders, and wherein means are provided for securing the inner, center and outer members to said base member. 
     
     
       11. An air-bearing center-guiding apparatus according to claim 10, wherein said inner, center and outer members comprise rings and said curved sides of said guide apertures are formed in the inner and outer end surfaces of the inner and outer rings and the straight sides of the circular segments are formed by the end surfaces of the center ring. 
     
     
       12. An air-bearing center-guiding apparatus according to claim 11, wherein the web enters the apparatus at a leading tangency line, wraps around a portion of the center ring, and leaves the apparatus at a trailing tangency line, and wherein the web-support means comprises two circumferentially extending rows of support apertures interposed between said rows of guide apertures in the wrap-around portion of the center ring for generating a predetermined volume of support air, and wherein three further circumferentially extending rows of support apertures are interposed between said rows of guide apertures at said leading and trailing tangency lines of the web, for generating a volume of support air greater than said predetermined volume. 
     
     
       13. An air-bearing center-guiding apparatus according to one of claims 1-12, wherein said inner, outer and center members are substantially cylindrical and the diameter of said inner and outer members is less than that of said center member, whereby said guide apertures are recessed below said web-facing surface. 
     
     
       14. An air-bearing center-guiding apparatus according to one of claims 1-12, wherein said curved side is shaped as a segment of a circle.